Discharge lamps are nowadays used in many sectors, for example as projection light sources.
In this case, a discharge lamp always comprises a bulb or burner, for example made from quartz glass, which has a burner chamber filled with gas. This burner chamber, the so-called drum, which is filled, for example, with xenon, other noble gases or metal vapors, for example mercury, contains two mutually opposite electrodes, between which the discharge takes place.
The geometric shape of known bulbs has been developed historically and optimized empirically. In particular, for reasons of manufacture, both the outer contour of the bulb and the shape of the drum are always rotationally symmetrical with respect to the bulb axis.
With the bulb according to the prior art, both the outer contour of the bulb and the drum have a central region, which is toroidal. This means that the section through one of these central regions with any desired plane containing the bulb axis is a circle segment having the radius r, whose midpoint has a distance R with respect to the bulb axis. In previous bulb designs, the midpoint of this circle segment is between this circle segment and the bulb axis (R>0).
The midpoints of the circle segments belonging to the central regions of the outer contour of the bulb and the drum are in this case in the same normal plane with respect to the bulb axis, with the result that the two toroids are concentric.
These central regions merge continuously with edge regions with mirror symmetry with respect to this normal plane, said edge regions being in the form of a truncated cone in the case of the drum, and tubular in the case of the outer contour. There is a constriction having predetermined radii between the central and the tubular region of the outer contour.
With known bulbs, both the outer contour and the shape of the drum are therefore always not only rotationally symmetrical with respect to the bulb axis but also have mirror symmetry with respect to the normal plane.
These symmetries are particularly advantageous when producing the bulb from glass, in particular quartz glass, and also bring about a high mechanical strength with respect to the gas pressure in the drum.
With known bulbs having the above-described geometrical shape, the optical efficiency, i.e. the ratio of consumed current to output light, is not yet optimal, however.